Page 1 of 1

Sunday improvisation

Posted: Sat Aug 09, 2008 8:32 pm
by Neo
Hi All,

Last Sunday had me fitting a new rear tyre to my daughters bike. Only to discover that the previous owner had fitted an inner tube. That left me short of a Tubeless valve stem to fit to the rim band/rim.
Being Sunday I had no choice but to improvise to get the job done. So I cut the old valve stem (and a some surrounding rubber) out of the inner tube. I then removed the nut (that would normally be on the inside of the rim) and use this valve Stem instead of the proper Tubeless valve stem.......and it's worked a treat :lol:

Anyway it occurred to me that at some time we must have all used these "Bush Mechanic" type of solutions when we just had to get the job done and couldn't get hold of the right parts.
So here's your opportunity to share what you did and how you did it with the Trials community =D>

Best of balance.


Re: Sunday improvisation

Posted: Sat Aug 09, 2008 9:10 pm
by David Lahey
I was about 16 and the piston in my Bultaco 325 Alpina was pretty worn and rattly. Compression was OK. My Dad had seen piston skirts knurled in much bigger motors (aircraft piston engines) to resize them and had an idea. I pulled the barrell off and my Dad reckoned that if the piston skirt could be resized, it would be much quieter while I saved up for a rebore and new piston.
We resized the skirt by making a steel dolly that fitted against the inside of the skirt and carefully centrepunched the outside of the skirt about 100 times on the front and back skirts.
This worked a treat. The motor was nice and quiet for about a month, then it suddenly started making a terrible piston rattle. Pulling it apart again, I found a crack that ran up from the bottom of the skirt about 20mm. There was also a small piece of skirt missing (broken off) from beside where the crack met the bottom edge.
I still couldn't afford a new piston yet so my Dad made a 3/32" thick patch from sheet duralumin and we riveted it on the inside of the skirt using hand driven aluminium rivets. The rivets were countersunk heads with the countersink end on the outside.
The bike ran fine for ages after that till I could finally afford the new piston and rebore.
I have kept the old piston (33 years so far) as a reminder of what you can do if you have to to keep a bike going.
I'll post a photo of it in the next few days.

Re: Sunday improvisation

Posted: Sun Aug 10, 2008 1:04 pm
by David Lahey
This is the Alpina piston with the patch on the skirt

Re: Sunday improvisation

Posted: Mon Aug 11, 2008 10:35 am
by gordonmichaellee
I once fixed a puncture with a peice of innertube tied in a not then shoved through the hole ( filed out first ) with plenty of butyl glue ( the punture repair stuff ) then trimed it with a knife. it did such a good job I never bothered to fix it any better.

Re: Sunday improvisation

Posted: Wed Aug 13, 2008 5:28 pm
by keithj
David Lahey wrote:This is the Alpina piston with the patch on the skirt


^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^ ^W^


Re: Sunday improvisation

Posted: Mon Sep 01, 2008 6:04 pm
by bigal
I have a friend who had rattly pistons on a Yamaha twin road bike. He used to put a piece of roundbar in a vice and with a shot pein hammer, carefully dinted the skirt. He said it expanded the shirt. He also filed off the intake and exhaust edges on top of the piston to effectively open the ports for a longer period. Seemed to work ok.


Re: Sunday improvisation

Posted: Sat Oct 04, 2008 6:06 pm
by brt650
Hello Everyone-I'm new here.
The great part to the piston story is-you have the piston to back up what you've said.How many times do you here stories that can't be real.
Anyway hope to see some of you on the track.
Brian :D